EN
Three sets of sequences of cytochrome oxidase subunit I (COI) from a spring snail Bythinella representing all the Balkans (63 sequences), Greece (78 sequences), and Romania (136 sequences), were used to infer maximum likelihood ultrametric trees. The trees were used to run General Mixed Yule Coalescent (GMYC) analyses assuming single threshold and multiple threshold models. For the single threshold model the threshold value was identical (0.00248 substitution per site) for each data set; for the multiple one the threshold value varied widely for the Balkan tree. Despite the same threshold value, the distinctness of the same lineages varied among trees, mostly due to differences in the models of substitution inferred for each set of sequences, but also due to different proportions of singletons in the data sets. The inferred numbers of ML entities, theoretically equalling the numbers of species, compared with all the biological evidence available so far, were overestimated in Romanian and Greek trees, but realistic in the tree for all the Balkans.